Friction and its types

Physics

example

Rolling Friction

A solid sphere of mass is placed on a rough inclined plane as shown in the figure. The coefficient is insufficient to start pure rolling. The sphere slides a length on the incline from rest and its kinetic energy becomes . Then, the work done by friction will be given by:
Work done by friction + Work done by gravity + work done by normal force = Kinetic energy
(Work energy theorem)
work done by normal force=0
Work done by gravity is mglsin
Work done by friction =

definition

Static Friction

Static friction is the force which acts between two bodies when a force is applied on a body but there is no relative motion between the surfaces. Static friction opposes an impending motion. It is denoted by . Law of static friction is given by:

where is the coefficient of static friction and depends only on the nature of the surfaces in contact. is the normal force.

definition

Sliding Friction

The Sliding Friction is friction which comes into play when surface of one object moves relative to surface of another object. It is also called as kinetic friction. It is that force that keeps a surface sliding with another surface. For example, if book is kept on floor and the book moves with respect to the floor.

It is the frictional force between two surfaces that are rubbing against each other. It’s hard to find a perfectly smooth surface in the real life, therefore when an object slides on any surface, it undergoes a backward force because of the relative motion between the two adjacent surfaces. It always acts against the motion. 

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What is Rolling Friction?

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Important Questions

State two advantages and disadvantages of friction.

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Mention the methods used to decrease friction

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Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below.
Choose the correct arrangement.

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A marble block of mass 2kg lying on ice when given a velocity of is stopped by friction in 10s. Then the coefficient of friction is ( Take )

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A block weighing 20N rests on a horizontal surface. The coefficient of static friction between the block and surface is 0.4 and the coefficient of kinetic friction is 0.20.
a. How much is the friction force exerted on the block?
b. How much will the friction force be if a horizontal force 5N is exerted on the block?
c. What is the minimum force that will start the block in motion?
d. What is the minimum force that will keep the block in motion once it has been started?
e. If the horizontal force is 10N, what is the friction force?

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Starting from rest ,a body slides down a 45 inclined plane in twice the time takes to slide down the same distance in the absence of friction .The coefficient of friction between the body and inclined plane is

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A block of mass lies on a horizontal surface in a truck, the coefficient of static friction between the block and the surface is . What is the force of friction on the block if the acceleration of the truck is ?
(Take )

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A 50 kg crate is being pushed across a horizontal floor by a horizontal force of 575 N. If the coefficient of sliding friction is 0.25, what is the acceleration of the crate ?

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It is easier to pull a lawn roller then to push it because pulling:

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Which one of the following statements is incorrect?

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